Optoelectronic device for acquisition of images, in particular of bar codes

ABSTRACT

An optoelectronic device for acquisition of images, such as images of bar codes, includes a case which contains an electronic scanning sensor, an illumination source and optics including a diaphragm that permit the formation of images on the sensor. The optics include at least two diopters disposed between the diaphragm and the sensor. For example, the diopters may take the form of a revolved symmetrical lens, the useful part of which is convex, and a cylindrical lens which does not create any deflection in a plane parallel to the optical plane, and is convergent in a plane perpendicular to the parallel plane.

The invention relates to an optoelectronic device for acquisition ofimages, in particular of bar codes.

The present optoelectronic devices which are designed for reading of barcodes conventionally comprise a case which contains an electronicscanning sensor, optical means which comprise a diaphragm, and make itpossible to form images on the sensor, and to define an optical planetogether with the latter, and electro-luminescent diodes which aredesigned to light the bar codes, and to permit acquisition of the imageson the sensor. Finally, these devices comprise processing electronicswhich permit piloting of the sensor, and processing of the signalsobtained from the latter.

In the conventional optoelectronic devices, the diaphragm has a circularaperture with a small diameter, such as to prevent defocussing of theimage, and/or to increase the depth of field of the device. However, asa result of the small diameter of this aperture, the light intensity,which is reflected by the bar code and reaches the sensor, is reduced,and in practice this fact makes it necessary to use light sources whichhave high light intensity, such as to compensate for the reduction oflight intensity.

It should be noted that it has been envisaged to increase the diameterof the aperture of the diaphragm, in order to increase the irradiance onthe sensor. However, this solution leads to reduction of the depth offield of the device, and thus to reduction of the efficiency of thelatter.

In order to eliminate these disadvantages, one solution consists ofproducing an optoelectronic device, as described in patent applicationEP 61000, the diaphragm of which has an aperture with a longitudinalaxis which is at right-angles relative to the axis of the bar codes,such as an aperture which has a rectangular, rhomboid or ellipticalshape.

In practice this solution makes it possible to increase the sensitivityof the optoelectronic devices, in proportion with the ratio of flowreceived relative to flow reflected. By this means, the depth of fieldof these devices is increased, without effecting substantially theintensity received on the sensor, and the efficiency of these devices isthus increased.

However, as a result of the relatively large dimensions of the apertureof the diaphragm, a solution of this type makes it necessary to useoptical means for formation of the image on the sensor, which are largerthan those of the conventional optical means, and which are thus morecostly and complex to produce than those of the conventional opticalmeans.

Another solution consists of producing optoelectronic devices asdescribed in international patent application WO-9620454, comprising twodioptres at right-angles relative to one another, which are disposedbetween the diaphragm and the optical sensor, and are designed toobtain, in the optical plane (XOZ) parallel to the optical plane,enlargement ml which is greater than the enlargement m2 in the plane(YOZ) perpendicular to the optical plane.

A solution of this type, which can also be associated with that which isdescribed in patent EP-61000, has optical means with characteristicswhich lead to an increase, according to axes which are parallel to thebar codes, in the dimension of the lit surface of the said bar codes,the image of which is reflected on the sensor, and thus to an increasein the sensitivity of the optoelectronic device.

It should also be noted that since this increase in the sensitivity ofthe device is obtained simply from the design of the optical means, andnot from the dimensions of the aperture of the diaphragm, a device ofthis type can be equipped with a conventional diaphragm with a circularaperture which has small dimensions, and thus with optical means withconventional dimensions, which are cheap and easy to produce.

However, as specified in the patent application in question on page 39,lines 23-24, with reference to FIG. 53, the optical means which make itpossible to obtain this result are very problematic to produce, whichhas led the inventor to abandon this solution, and to propose adifferent solution.

The object of the present invention is to eliminate this disadvantage,and its main objective is to obtain enlargement m1 in planes (XOZ)parallel to the optical plane, which is greater than the enlargement m2in a plane (YOZ) perpendicular to the said optical plane, by usingoptical means which are in common use and are easy to produce.

For this purpose, the invention relates to an optoelectronic device foracquisition of images, in particular of bar codes, comprising a casewhich is provided with a reading window, and contains an electronicscanning sensor, lighting means, and optical means which comprise adiaphragm, and are designed to ensure that images are formed on thesensor, and to obtain, in a plane (XOZ) parallel to the optical plane,enlargement m1 which is greater than the enlargement m2 in a plane (YOZ)perpendicular to the said optical plane, the sensor and the opticalmeans defining an optical plane relative to which the reading window iscentred, and the said sensor, reading window and optical meansdelimiting a useful optical reading field.

According to the invention, the optical means comprise:

first optical means, comprising a first, converging lens, consisting ofa symmetrical lens which is revolved around the optical axis, the usefulpart of which is convex; and

second optical means, comprising a so-called cylindrical lens with asemi-cylindrical dioptre, which is designed not to create any deflectionin the plane (XOZ) parallel to the optical plane, and to converge in theplane (YOZ) perpendicular to the said optical plane.

According to the invention, the enlargement m1/m2 is obtained by meansof lenses with a conventional design, i.e.:

a first symmetrical lens which is revolved by means of a simpleconventional turn; and

a second, cylindrical conventional lens, of a design which is commonlyavailable.

The invention thus leads to the same advantages as those described onpage 39 of patent WO-9620454, whilst leading to conventional productionof the optical means, the cost price of which does not make the cost ofthe optoelectronic device disadvantageous.

However, it has been found that although use of optical means whichconsist of a symmetrical lens which is revolved, and a cylindrical lens,lead to perfect results when the optoelectronic device is perfectlyaligned with the bar code (product which is passed in front of a fixedoptoelectronic device, etc), the astigmatism which optical means of thistype introduce increases the sensitivity to errors of rotation aroundthe optical axis.

For this reason, and according to another characteristic of theinvention, the optical means additionally comprise a correction lens,which is associated with the first optical means. It should be notedthat the construction of this correction lens is easy, since it isneutral in the plane XOZ in which the bar code is used.

In fact, the solution preferably consists of using a single- ormultiple-component symmetrical lens which is revolved, which isassociated with a cylindrical lens which has a meniscal-type profile foropposite enlargement, which is designed to cancel out the optical powerin the plane (YOZ). This therefore retains the optical quality which iscommonly achieved for symmetrical revolving optics necessary in theplanes (XOZ). It should also be noted that the assembly of the mainlens/correction lens must be optimised as a whole, since the cylindricallens introduces an astigmatism at the edges of the fields.

Thus, the correction lens, which advantageously consists of a simpleflat/concave cylindrical lens, constitutes a correction component whichmakes it possible to solve the problems of rotation, whilst maintainingthe advantage of leading to an increase in the sensitivity of thedevice.

In practice, experiments have thus made it possible to show that the barcode can be inclined by an angle greater than 10°, before the MTF(Modulation Transfer Function) is reduced significantly.

According to another characteristic of the invention, the optical meansare designed so that the ratio of m1/m2 is such that 3<m1/m2<5.

In fact, this ratio range constitutes a good compromise for theperformance of the optoelectronic device, which leads to a substantialincrease of the sensitivity of the latter relative to the presentconventional devices, without however detracting from the functioning ofthe said device, if it is positioned in front of the object which isbeing rotated around the optical plane (XOZ).

According to another characteristic of the invention:

the ratio of the enlargement m1/m2 of the first and second optical meansis such that m1/m2 is greater than 1; and

the first optical means are disposed in the vicinity of the diaphragm,between the said diaphragm and the second optical means.

In addition, the lens which is revolved is advantageously of theaspherical type, and has the shape of an ogive, such as to preventgeometric aberrations.

According to a further characteristic of the invention, the linearsensor and the diaphragm are disposed such that they are centred on axesat right angles relative to one another, a mirror which is inclined byan angle of 45° relative to the said axes being positioned such as toreflect the images on the said sensor.

This arrangement has the advantage that it leads to a reduction in thesize of the optical means, and thus to optimisation of the size of thecase.

According to a further characteristic of the invention, the diaphragmhas an aperture with a dimension in the direction Y which is greaterthan that in the direction X. This leads to an increase in thesensitivity of the device or the depth of field.

Other characteristics, objects and advantages of the invention willbecome apparent from the following detailed description provided withreference to the attached drawings, which represent a non-limitingexample of a preferred embodiment. In the drawings which are an integralpart of the present invention:

FIG. 1 is a perspective view of an optoelectronic device according tothe invention;

FIG. 2 is a longitudinal cross-section through an axial plane A;

FIG. 3 is an exploded perspective view of the main components containedin the case of this optoelectronic device;

FIG. 4 is a perspective view of a lens which constitutes the firstoptical means of this device;

FIG. 5 is a longitudinal cross-section through a plane C of this lens;

FIGS. 6a and 6 b are skeleton diagrams which represent the path of theimage beams according to two planes (YOZ) and (XOZ) which are atright-angles relative to one another; and

FIG. 7 represents the lit object surface, the image of which isreflected on the sensor, and the corresponding image of this surface onthe said sensor;

FIG. 8 is a schematic diagram showing the relative magnification in theX and Y directions.

The optoelectronic device shown in FIGS. 1 and 2 consists of a bar codereader which is in the form of a case which is elbowed longitudinally,consisting of two shells 1, 2 which can be assembled by any known means,and a rear joining piece 3 which can be dismantled, and makes itpossible to access a receptacle 4 for a battery 5.

At its front surface, the case additionally comprises an aperture 6,which is closed by a transparent window 7.

This case also comprises a longitudinal trigger 8, which extends throughan aperture which is provided in the lower shell 2, and is articulatedtowards the rear end of the said shell.

Inside this case there is accommodated an electronic card 9, to whichthere are connected firstly a linear CCD sensor 10, and conventionalelectronic processing and decoding components which permit piloting ofthe said sensor, and processing of the signals obtained from the latter.

There is also connected to this electronic card 9 a switch 11, which isdisposed such that it can be actuated by the trigger 8.

The optical means of this reader are disposed inside a case 12, closedby a cover 13, which is rendered integral with the said case by means ofscrews 14. This case 12 additionally comprises four locking lugs such as15, 16, which project relative to its front and rear walls, and aredisposed such that they snap into notches such as 17,18 provided in theelectronic card 9.

On its under-surface, and juxtaposed with the front surface of its rearwall, the case 12 additionally comprises a receptacle 19 for the CCDsensor 10, which is separated from the interior of the said case bymeans of a flat wall 20, which contains a transverse slot 20 a.

The optical means comprise firstly a lens 21 which is so-calledcylindrical, i.e. which has a dioptre with a semi-cylindrical shape, andis disposed transversely in a receptacle 22 of the case 12, which issuperimposed on the receptacle 19 for the CCD sensor 10. This lens 21has a 6 mm focal length, and is disposed at a distance of approximately2.5 mm from the CCD reader 10.

As shown in FIGS. 6a and 6 b, a lens of this type does not give rise todeflection of the light rays in a plane which is parallel to the opticalplane, and is convergent in a plane which is perpendicular to theoptical plane.

The optical means additionally comprise a mirror 23 which is inclined by45° relative to the lens 21, and is rendered integral with theunder-surface of a wall of the cover 13, which itself is inclined by45°.

As shown in FIGS. 5, 6 a and 6 b, the optical means also comprise asymmetrical lens 40 which is revolved, the useful part 40 a of which canbe semi-cylindrical or convex, and is fitted into slots which areprovided opposite in the case 12 and cover 13.

These optical means also comprise a correction lens 50, consisting of asurface which has a radius of curvature of 7.5 mm.

Finally, these optical means comprise a diaphragm 25, which is providedwith a circular entrance pupil with a diameter of 4.5 mm, which isdisposed at a distance of 58 mm from the lens 21, and is fitted intogrooves which are provided opposite in the case 12 and cover 13.

As shown in FIGS. 6a, 6 b, 7, and 8 optical means of this type make itpossible to “enlarge” according to the axis Y which is perpendicular tothe optical plane, the dimension of the lit surface of the bar codes,the image of which is reflected on the sensor, and consequently make itpossible to increase the sensitivity of the reader.

The means for lighting the reader are disposed directly downstream fromthe case 12. Firstly, they comprise four attached electro-luminescentdiodes such as 26, which have an angle of diffusion of 125°. These fourdiodes 26 are connected to the electronic card 9, and are alignedaccording to an axis which is at right-angles relative to the opticalaxis.

These lighting means additionally comprise a convex lens 27 forfocussing the light beam, in planes which are respectively parallel to,and perpendicular to the optical axis.

Firstly, this lens 27 comprises a flat dioptre, which is provided with arecess 28, which has a shape suitable for accommodating the diodes 26.In addition, this recess 28 is filled with a resin which has the sameindex of refraction as the lens 27.

This lens 27 additionally comprises two pins such as 29, which projectrelative to the flat dioptre of the lens, and allow the lens to befitted onto the electronic card 9.

Finally, this lens 27 comprises a convex dioptre with a toroidal shape,which has two radii of curvature, respectively of 20 mm and 3.25 mm.

Finally, the lighting means comprise reflection means, which aredisposed such as to intercept the light beams of the diodes 26, areinclined by an angle of 45°, and are designed such that the said lightbeams are centred on the optical axis.

These reflection means consist of a mirror 30, which is provided with atransverse slot 31 which allows the image beam to pass through, and inits upper part has a stiffening edge 30 a. This mirror 30 is alsoconnected to a support plate 32 by means of a tab 33, which acts as anaxis of articulation between the said mirror and support plate.

This support plate 32 is designed to be accommodated in spaces providedbetween the front wall of the case 12 and the locking lugs 16, such thatthe slot 31 of the mirror 30 is centred on the optical axis, in whichposition the said slot is as close as possible to the diaphragm.

In addition, two screws, such as 34, each of which is disposed in athreaded bore provided in an arm such as 35, which projects relative tothe front wall of the case 12, are designed to be supported on themirror 30, such as to permit adjustment of the inclination of thelatter, and/or to make it pivot relative to the support plate 32, inorder to superimpose the light beam on the optical plane.

What is claimed is:
 1. An optoelectronic device for acquisition of images, in particular of bar codes, comprising a case which is provided with a reading window, and contains an electronic scanning sensor, lighting means, and optical means which comprise a diaphragm, and are designed to ensure that images are formed on the sensor, and to obtain, in a plane parallel to the optical plane, enlargement m1 which is greater than the enlargement m2 in a plane perpendicular to the optical plane, the sensor and the optical means defining an optical plane relative to which the reading window is centered, and the said sensor, reading window and optical means delimiting a useful optical reading field, wherein the optical means comprise, disposed between the diaphragm and the sensor: first optical means, comprising a first, converging lens, consisting of a symmetrical lens which is revolved around the optical axis, the useful part of which is convex; and second optical means, comprising a cylindrical lens with a semi-cylindrical diopter, which is designed not to create any deflection in the plane parallel to the optical plane, and to converge in the plane perpendicular to the said optical plane.
 2. The optoelectronic device as claimed in claim 1 wherein the first optical means comprise a correction lens, which is associated with the cylindrical lens which is revolved.
 3. The optoelectronic device as claimed in claim 1 wherein the optical means are designed so that the ratio of m1/m2 is such that 3<m1/m2<5.
 4. The optoelectronic device as claimed in claim 1 wherein: the ratio of the enlargements m1/m2 of the first and second optical means is such that m1/m2 is greater than 1; and the first optical means are disposed in the vicinity of the diaphragm, between the said diaphragm and the second optical means.
 5. The optoelectronic device as claimed in claim 1 wherein the lens which is revolved is of the aspherical type, and has the shape of an ogive.
 6. The optoelectronic device as claimed in claim 1 wherein the sensor and the diaphragm are disposed such that they are centered on axes at right angles relative to one another, a mirror which is inclined by an angle of 45° relative to the said axes being positioned such as to reflect the images on the said sensor.
 7. The optoelectronic device as claimed in claim 1 wherein the diaphragm has an aperture in the direction (Y) which is greater than that in the direction (X).
 8. An optics system for an optoelectronic imager, comprising: a diaphragm; a cylindrical lens positioned after the diaphragm along an optical path; a converging lens positioned between the diaphragm and the cylindrical lens along the optical path, where the combination of the cylindrical lens and converging lens combine to produce an image having a first magnification in a first plane and a second magnification in a second plane, the second plane being substantially perpendicular to the first plane and the first magnification being greater than the second magnification; and a corrective lens positioned along the optical path.
 9. The optics system of claim 8 comprising: an optical sensor positioned after the cylindrical lens along the optical path, the optical sensor having an optical plane substantially parallel to the first plane.
 10. The optics system of claim 8, further comprising: a mirror positioned after the cylindrical along the optical path; and an optical sensor positioned after the mirror along the optical path, the optical sensor having an optical plane substantially parallel to the first plane.
 11. An optoelectronic device for imaging, comprising: a housing having a window formed therein; an elongated optical sensor received in the housing, the optical sensor having a length and a width where the length is greater than the width; a diaphragm received in the housing between the window and the sensor and the optical sensor; and an optical lens system received in the housing between the window and the optical sensor, the optical lens system having a first magnification factor along a first axis substantially parallel to the length of the optical sensor and a second magnification along a second axis substantially parallel to the width of the optical sensor, where the ratio of the first magnification to the second magnification is greater than
 1. 12. The optoelectronic device of claim 11 wherein the ratio of the first magnification to the second magnification is greater than 3 and less than
 5. 13. The optoelectronic device of claim 11 wherein the optical lens system comprises: a converging lens received in the housing between the diaphragm and the optical sensor; and a cylindrical lens received in the housing between the converging lens and the optical sensor.
 14. The optoelectronic device of claim 11 wherein the optical lens system comprises: a converging lens received in the housing between the diaphragm and the optical sensor; a mirror received in the housing between the converging lens and the optical sensor; and a cylindrical lens received in the housing between the mirror and the optical sensor.
 15. The optoelectronic device of claim 11, further comprising: a converging lens received in the housing between the diaphragm and the optical sensor; a mirror received in the housing between the converging lens and the optical sensor; a cylindrical lens received in the housing between the mirror and the optical sensor; and a correction lens received in the housing between the window and the diaphragm, the correction lens being shaped to cancel at least a portion of the magnification of the combination of the converging and the cylindrical lenses along the second axis.
 16. The optoelectronic device of claim 11, further comprising: a converging lens received in the housing between the diaphragm and the optical sensor; a mirror received in the housing between the converging lens and the optical sensor; a cylindrical lens received in the housing between the mirror and the optical sensor; and a flat/concave cylindrical correction lens received in the housing between the window and the diaphragm, the correction lens matched with the converging lens to be substantially neutral with respect to the magnification of the combination of the converging and the cylindrical lenses along the first axis and to cancel at least a portion of the magnification of the converging and the cylindrical lens combination along the second axis.
 17. The optoelectronic device of claim 11, further comprising: a converging lens received in the housing between the diaphragm and the optical sensor; a mirror received in the housing between the converging lens and the optical sensor, wherein the converging lens is ogive shaped; and a cylindrical lens received in the housing between the mirror and the optical sensor.
 18. An optoelectronic device for imaging, comprising: a housing having a window formed therein; an optical sensor received in the housing, the optical sensor having an optical plane for receiving light therealong; and an optical lens combination received in the housing between the window and the optical sensor, the optical lens combination having a first magnification in a first plane parallel to the optical plane and a second magnification in a second plane perpendicular to the optical plane, where a ratio of the first magnification and the second magnification is greater than
 1. 19. The optoelectronic device of claim 18, further comprising: a diaphragm received in the housing along an optical path extending between the window and the optical sensor. 